A typical inkjet printing apparatus discharges visual ink droplets in cyan (C), magenta (M), yellow (Y), and black (K) from individual printing head to a printing sheet for printing images. In addition, an overcoating agent is applied to a printing sheet, especially to a coated paper, after image printing to obtain an enhanced texture after printing such as a feeling of glossiness or enhanced friction resistance. It is presupposed that the overcoating agent is applied to an image region printed in advance. A transparent (invisible) material is discharged as the overcoating agent from a printing head having an identical construction to that used for the individual visible color.
Here, the overcoating agent is transparent. Accordingly, it is difficult on the printing sheet to visually confirm whether or not the overcoating agent is discharged from all nozzles of an overcoating printing head. Consequently, such an apparatus as under has been suggested for confirming application of the overcoating agent. That is, for confirming discharge of the overcoating agent, an overcoating agent is applied and thereafter an image recognition camera recognizes the overcoating agent. Examples of the overcoating agent include an overcoating agent sensitive to fluorescence or infrared light and an overcoating agent containing an ultraviolet absorbing additive agent. See, for example, Japanese Patent Publication No. 2003-251243A.
However, the example of the currently-used apparatus with such a construction as above has the following drawback.
That is, the currently-used apparatus possesses a drawback that a special overcoating agent and an image recognition camera result in an increased apparatus cost.